Radiation therapy can be used to treat localized cancer. In a typical application, a radiation delivery system has an ionizing radiation device mounted to a movable gantry. The radiation delivery system controls the motion of the radiation device to direct an ionizing radiation beam to a specific point in space commonly referred to as the “machine isocenter.”
One aspect of radiation therapy is positioning a patient so that the patient's tumor is located at the machine isocenter during treatment. Conventional patient positioning systems use various technologies to locate the tumor, including optically locating visual markers applied to the patient's skin, or using X-ray imaging to locate metal fiducials subcutaneously implanted in the patient. Conventional patient positioning systems are typically used only to align patients in preparation for the delivery of radiation energy.
To ensure that radiation energy is delivered to a patient's tumor as planned, though, it would be useful to provide patient location information during the delivery of radiation energy. It can be difficult to successfully apply conventional approaches to patient tracking to provide patient location information during the delivery of radiation, however.
Using conventional X-ray based tracking techniques, each tracking measurement exposes the patient to an additional dose of X-ray imaging radiation. Were the use of X-ray based tracking expanded to operate throughout the course of radiation therapy, the patient would be exposed to potentially harmful levels of X-ray imaging radiation. Additionally, in some implementations, the delivery of energy during radiation therapy can interrupt the efficacy of X-ray based tracking techniques. For instance, the presence of radiation therapy radiation may interfere with the sensing of imaging radiation. As another example, the presence of the X-ray imaging emitter and/or sensor may physically interrupt the radiation treatment energy beam.
It can also be difficult to successfully apply conventional optical tracking techniques during the delivery of radiation. Here too, the presence of optical tracking sensors may interrupt the radiation treatment energy beam. Conversely, radiation treatment equipment may intervene between the patient and the optical tracking sensors, blocking their view of the patient. Also, as optical tracking techniques typically rely on 2-dimensional tracking of the exterior surface of the patient's body, their accuracy depends on the consistency of such factors as the shape of the exterior surface of the patient's body, and the location of the tumor relative to the locations of the visual markers. Because these factors are inherently variable, positioning data obtained using conventional optical tracking techniques can be inaccurate.
In view of the foregoing, a patient tracking system that provided useful patient tracking information during the delivery of radiation energy, and that promptly acted on such information, would have significant utility.
In the drawings, identical reference numbers identify similar elements or components. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. For example, the shapes of various elements and angles are not drawn to scale, and some of these elements are arbitrarily enlarged and positioned to improve drawing legibility. Further, the particular shapes of the elements as drawn, are not intended to convey any information regarding the actual shape of the particular elements, and have been solely selected for ease of recognition in the drawings.